It has long been desirable to increase the efficiency of internal combustion engines, particularly engines utilized in automobiles and the like. In order to increase the efficiency of such an engine, it is desirable to reduce mechanical loss within the engine and to improve the efficiency of combustion of the fuel itself.
The conventional four stroke internal combustion engine utilizes an intake stroke, compression stroke, combustion stroke, and exhaust stroke. During the compression stroke, it is important, in order to accomplish complete combustion of the fuel/air mixture provided to the cylinder, to improve the propagation of combustion through the cylinder from the spark plug and to ensure that the air/fuel mixture is as close as possible to the so-called stoichiometric point.
One method to improve fuel combustion is to ensure that the freshly introduced mixture is not contaminated with burnt and unburnt gases incompletely exhausted during the exhaust stroke of a normal internal combustion cycle. Such burnt and unburnt gases deteriorate the propagation of flame throughout the fresh charge mixture and thus, inhibit the efficiency of the engine.
One solution to this problem was proposed in Japanese laid-open application no. 212326/82, published on Dec. 27, 1982 and assigned to the assignee of the present application, which discloses an internal combustion engine utilizing a conventional two-stroke combustion process for a first process and utilizing fresh mixture inducted into the combustion chamber to flush the burnt and unburnt gases from the combustion chamber in a second process.
In this system which uses a two-stroke type internal combustion process for the first process, even if the mixture supply passage and the air supply passage are independent, air for the second process is introduced into the cylinder through a scavenging passage right after being introduced into the crankcase. Since the crankcase has a large volume sized similarly to that of the cylinder displacement, the fresh air is mixed with the remaining mixture of the prior stroke during the scavenging process, resulting in the use of a mixture of fresh air and remaining air/fuel mixture, and thus, does not provide the sought after degree of improvement in fuel efficiency. Furthermore, as the fresh air is supplied into the cylinder after being compressed in the crankcase, substantial mechanical loss exists.